Parthenogenesis without costs in a grasshopper with hybrid origins.

The rarity of parthenogenetic species is typically attributed to the reduced genetic variability that accompanies the absence of sex, yet natural parthenogens can be surprisingly successful. Ecological success is often proposed to derive from hybridization through enhanced genetic diversity from repetitive origins or enhanced phenotypic breadth from heterosis. Here, we tested and rejected both hypotheses in a classic parthenogen, the diploid grasshopper Warramaba virgo. Genetic data revealed a single hybrid mating origin at least 0.25 million years ago, and comparative analyses of 14 physiological and life history traits showed no evidence for altered fitness relative to its sexual progenitors. Our findings imply that the rarity of parthenogenesis is due to constraints on origin rather than to rapid extinction.

Best practices for building and curating databases for comparative analyses.

Comparative analyses have a long history of macro-ecological and -evolutionary approaches to understand structure, function, mechanism and constraint. As the pace of science accelerates, there is ever-increasing access to diverse types of data and open access databases that are enabling and inspiring new research. Whether conducting a species-level trait-based analysis or a formal meta-analysis of study effect sizes, comparative approaches share a common reliance on reliable, carefully curated databases. Unlike many scientific endeavors, building a database is a process that many researchers undertake infrequently and in which we are not formally trained. This Commentary provides an introduction to building databases for comparative analyses and highlights challenges and solutions that the authors of this Commentary have faced in their own experiences. We focus on four major tips: (1) carefully strategizing the literature search; (2) structuring databases for multiple use; (3) establishing version control within (and beyond) your study; and (4) the importance of making databases accessible. We highlight how one's approach to these tasks often depends on the goal of the study and the nature of the data. Finally, we assert that the curation of single-question databases has several disadvantages: it limits the possibility of using databases for multiple purposes and decreases efficiency due to independent researchers repeatedly sifting through large volumes of raw information. We argue that curating databases that are broader than one research question can provide a large return on investment, and that research fields could increase efficiency if community curation of databases was established.

Linking thermal adaptation and life-history theory explains latitudinal patterns of voltinism.

Insect life cycles are adapted to a seasonal climate by expressing alternative voltinism phenotypes-the number of generations in a year. Variation in voltinism phenotypes along latitudinal gradients may be generated by developmental traits at critical life stages, such as eggs. Both voltinism and egg development are thermally determined traits, yet independently derived models of voltinism and thermal adaptation refer to the evolution of dormancy and thermal sensitivity of development rate, respectively, as independent influences on life history. To reconcile these models and test their respective predictions, we characterized patterns of voltinism and thermal response of egg development rate along a latitudinal temperature gradient using the matchstick grasshopper genus Warramaba. We found remarkably strong variation in voltinism patterns, as well as corresponding egg dormancy patterns and thermal responses of egg development. Our results show that the switch in voltinism along the latitudinal gradient was explained by the combined predictions of the evolution of voltinism and of thermal adaptation. We suggest that latitudinal patterns in thermal responses and corresponding life histories need to consider the evolution of thermal response curves within the context of seasonal temperature cycles rather than based solely on optimality and trade-offs in performance. This article is part of the theme issue 'Physiological diversity, biodiversity patterns and global climate change: testing key hypotheses involving temperature and oxygen'.

Summer egg diapause in a matchstick grasshopper synchronizes the life cycle and buffers thermal extremes.

The phenological response is among the most important traits affecting a species' sensitivity to climate. In insects, strongly seasonal environments often select for a univoltine life cycle such that one seasonal extreme is avoided as an inactive stage. Through understanding the underlying mechanisms for univoltinism, and the consequences of its failure, we can better predict insect responses to climate change. Here we combine empirical data and simulation studies to investigate the consequences of an unusual diapause mechanism in a parthenogenetic matchstick grasshopper, Warramaba virgo, from arid southern Australia. Our field body temperature measurements indicate that this species is a thermoconformer and our laboratory studies of the thermal response of feeding rate imply strong constraints on winter activity. However, the species exhibits no obligate winter diapause, and eggs can develop in 1 month under constant temperatures approximating the mean soil temperature at the time of oviposition (summer). We show that diurnal temperature cycles exceeding a peak of 36 °C inhibit egg development in summer, and that this is sufficient to prevent autumnal hatching of eggs. Development is also strongly retarded below 24 °C. Microclimate-driven simulation studies of egg development show that these thermal responses provide robust maintenance of a univoltine life cycle, thereby resulting in survival of heat stress as an egg (due to limited developmental state) and avoidance of cold stress as a nymph and adult (due to overwintering in the soil as an egg).

Mechanistic models for predicting insect responses to climate change.

Mechanistic models of the impacts of climate change on insects can be seen as very specific hypotheses about the connections between microclimate, ecophysiology and vital rates. These models must adequately capture stage-specific responses, carry-over effects between successive stages, and the evolutionary potential of the functional traits involved in complex insect life-cycles. Here we highlight key considerations for current approaches to mechanistic modelling of insect responses to climate change. We illustrate these considerations within a general mechanistic framework incorporating the thermodynamic linkages between microclimate and heat, water and nutrient exchange throughout the life-cycle under different climate scenarios. We emphasise how such a holistic perspective will provide increasingly robust insights into how insects adapt and respond to changing climates.